worktree.c: add is_main_worktree()

Main worktree _is_ different. You can lock (*) a linked worktree but not
the main one, for example. Provide an API for checking that.

(*) Add the file $GIT_DIR/worktrees/xxx/locked to avoid worktree xxx
from being removed or moved.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 10 insertions, 0 deletions

diff --git a/worktree.c b/worktree.c
index 0782e0098..12a766a38 100644
--- a/worktree.c
+++ b/worktree.c
@@ -229,6 +229,11 @@ struct worktree *find_worktree(struct worktree **list,
 	return *list;
 }
 
+int is_main_worktree(const struct worktree *wt)
+{
+	return !wt->id;
+}
+
 int is_worktree_being_rebased(const struct worktree *wt,
 			      const char *target)
 {
diff --git a/worktree.h b/worktree.h
index 7ad15da0d..e1c471523 100644
--- a/worktree.h
+++ b/worktree.h
@@ -38,6 +38,11 @@ extern struct worktree *find_worktree(struct worktree **list,
 				      const char *arg);
 
 /*
+ * Return true if the given worktree is the main one.
+ */
+extern int is_main_worktree(const struct worktree *wt);
+
+/*
  * Free up the memory for worktree(s)
  */
 extern void free_worktrees(struct worktree **);